The average spectral power distribution of a set of measured daylight spectra, $E_{\text{av}}(\lambda )$ , is used for preliminary screening to select optimal sensor sets for daylight recovery. Spectra quite different from $E_{\text{av}}(\lambda )$ are applied to the screened sets to obtain minimum total spectral error, which is closely related to recovery metrics but not to the coefficient of error. All basis functions should be utilized to make these two errors equal, to predict precisely the best sensor set, and to extend a set of few sensors to a set of many sensors. These are not acquirable by an exhaustive full search method.